vm-image: add sqlexporter for autoscaling metrics

[skyzh]

Problem

As discussed in neondatabase/autoscaling#895, we want to have a separate sql_exporter for simple metrics to avoid overload the database because the autoscaling agent needs to scrape at a higher interval. The new exporter is exposed at port 9499. I didn't do any testing for this pull request but given it's just a configuration change I assume this works.

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2856 tests run: 2735 passed, 0 failed, 121 skipped (full report)

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Flaky tests (2)

Postgres 16

• test_vm_bit_clear_on_heap_lock: debug

Postgres 15

• test_partial_evict_tenant[relative_equal]: release

Code coverage* (full report)

• functions: 28.1% (6601 of 23486 functions)
• lines: 46.8% (46863 of 100233 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
543c819 at 2024-05-01T14:07:08.125Z :recycle:}

[sharnoff]

re: testing- it would be good to test on staging, using a compute image built from CI. Feel free to ping me for details if unsure how.

[skyzh]

tested in staging:

> curl localhost:9499/metrics
# HELP lfc_approximate_working_set_size Approximate working set size in pages of 8192 bytes
# TYPE lfc_approximate_working_set_size gauge
lfc_approximate_working_set_size 269
# HELP lfc_cache_size_limit LFC cache size limit in bytes
# TYPE lfc_cache_size_limit gauge
lfc_cache_size_limit 6.30194176e+08
# HELP lfc_hits lfc_hits
# TYPE lfc_hits gauge
lfc_hits 0
# HELP lfc_misses lfc_misses
# TYPE lfc_misses gauge
lfc_misses 279
# HELP lfc_used LFC chunks used (chunk = 1MB)
# TYPE lfc_used gauge
lfc_used 66
# HELP lfc_writes lfc_writes
# TYPE lfc_writes gauge
lfc_writes 279